How popular is the following scenario?
The man kneels down at the table in an upper-class restaurant, utters a few sentimental words to his lady, she says yes, and the strangers around them deliver a concluding applause.

It's pretty popular. I would also say that public proposals are becoming the NORM.

In my opinion, private proposals should be the norm, because I can't see what the strangers add to the scenario. What purpose do they serve for this couple's special moment? If anything, public proposals have a subtle air of approval-seeking. A certain "look at me, I'm making a grown-up decision".

Agreed. Public proposals seem to be a thing for Americunts in particular. I think it's very wrong, it's exactly what an attention-whore would do who is seeking approval and praise from others. And that is exactly why they're doing it. If someone proposed to me in public, I would refuse just for that reason. You gotta have some dignity. I'm not sure why you would think it's becoming the norm, though. I see this crap a lot on TV, but I've never actually witnessed such a case first hand. Have you?

I've never witnessed a public proposal. It's something I've only seen on American TV.

I think largely it's a bit of blackmail. Nobody wants to sit with their lover in a large crowd full of their societal peers and turn down a heartfelt marriage proposal. It would make the decliner look like a total dick. If you propose to your partner in private, they can do anything from say yes and fuck you on the spot, to declining and kicking you in the groin for asking. In public, your options are much more limited, almost to the point where saying no makes you look like the bad guy - instead of the real bad guy, the person who put you on the spot in front of dozens (or thousands - Superbowl, anyone?) of people with the pressure on to say only yes or yes please.